1. Field of the Invention
The present invention pertains to a combined patient interface and integrated exhaust assembly, and, in particular, to such a combination in which the exhaust assembly provides a controlled flow of exhaust gas, such as a constant flow of gas, from the interior of the patient interface over a range of pressures within the patient interface relative to ambient atmosphere.
2. Description of the Related Art
Conventional exhaust assembles are used, for example, to provide an exhaust flow path for exhaled air in a ventilation circuit, which supplies a continuous flow of breathing gas to a spontaneously breathing patient. During the exhalation phase of the patient""s breathing, exhalation gas backflows in the ventilation circuit and, unless exhausted from the circuit, can be rebreathed by the patient during the next inhalation phase. Rebreathing of exhaled gas is undesirable, of course, because the exhalation flow contains CO2. Reliable and thorough exhaustion or purging of exhalation gas from the ventilation circuit is, thus, an important feature of such ventilation circuits, which are also commonly referred as breathing circuits or patient circuits. This purging becomes a more difficult problem the further the exhalation valve is located from the patient interface, due to the amount of residual exhaled gas in the intervening ventilation circuit dead space.
Most such exhalation valves provide varying fluid flow at varying fluid pressures. However, the naturally occurring relationship of fluid flow rate to pressure (flow is proportional to the square root of pressure) may be unacceptable in a ventilation circuit for a number of reasons. For example, in medical ventilators used to assist patient breathing, and in similar devises used to supply breathing gas to a spontaneously breathing patient, it has been common practice to include a fixed size leak, especially in single limb circuits, to flush away the gas that is exhaled by the patient into the breathing circuit before the exhaled gas can be rebreathed by the patient with the next inhalation. The fixed sized, i.e., fixed geometry or fixed orifice, leak may be provided by an exhalation valve. However, an exhalation valve with a flow characteristic that varies naturally with pressure variations in the patient circuit may not be suitable as a patient circuit exhaust valve.
Additionally, in the operation of such systems it is known to supply to a patient an exhalation pressure that is lower than the inhalation pressure. With many conventional exhalation valves, the size of the fixed leak needed to flush exhaled gas from the circuit under the relatively lower pressure of exhalation may be so large that the flow rate through the fixed leak at the higher inhalation pressure would result in enormous waste of supply gas during inhalation. Such conditions may also require a larger capacity pressure generator, commonly a blower, for example, than would otherwise be required. This too is wasteful in that the result is unnecessary added cost for the apparatus and increased energy consumption to operate it.
It is, therefore, preferable that the flow rate of the leak provided to flush exhaled gas from such a ventilation circuit does not change appreciably within the range of pressures applied in the circuit. In this sense, a fixed leak is more desirably one that provides a fixed flow rate, than one characterized by a flow path cross sectional area of fixed size.
Among the prior art of valves purporting to regulate flow by means of pressure actuated regulators are those disclosed in U.S. Pat. Nos. 3,467,136, 3,474,831, 3,592,237, 3,948,289 and 3,951,379. Other flow regulating valves are disclosed in U.S. Pat. Nos. 3,429,342, 3,473,571, 3,770,104, 4,182,371, 4,234,013, 4,280,527, 4,351,510 and 4,354,516. U.S. Pat. No. 4,428,397, apparently related German Patent no. DE 27 48 055 A1, and Russian Patent abstract SU 1015344A disclose a valve for controlling the rate of flow of fluid therethrough. In addition, U.S. Pat. No. 5,002,050 discloses a medical gas flow control valve and U.S. Pat. No. 5,438,981 discloses an automatic safety valve and diffuser for a nasal and/or oral gas delivery mask.
U.S. Pat. Nos. 5,685,296 and 5,937,855 disclose a flow regulating valve that exhausts gas from a ventilation circuit at a constant flow rate despite varying pressure in the ventilation circuit. However, as noted above, it may be further desirable to locate the exhaust valve at the mask, for example, so that the amount of ventilation circuit dead space is minimized and to eliminate the need to provide a relatively bulky exhaust structure on the ventilation circuit. In treating obstructive sleep apnea OSA, for example, a positive pressure therapy is provided to the patient while he or she sleeps. Therefore, it is preferable for the patient circuit to be flexible and readily movable during the pressure support treatment. This goal may be frustrated by providing the exhaust valve on the patient circuit. In the hospital setting, it is also preferable to minimize the entanglements on the patient circuit to keep as clear a working area as possible for the doctors and nurses.
Accordingly, it is an object of the present invention to provide a combined patient interface and integrated exhaust assembly that overcomes the shortcomings of conventional flow control valves. More specifically, the present invention contemplates a novel combination of a patient interface, such as a mask, and a flow control valve integrated with the mask and/or integrated with connection between the mask and the patient circuit. In a preferred embodiment of the present invention, the flow control valve exhausts gas from the mask at a constant gas flow rate over a range of pressures within the interface. Because the valve is incorporated into the breathing mask or similar apparatus, which confronts the face of the patient, the amount of dead space in the patient circuit is minimized, and there is no excess material on the patient circuit that can hinder its performance or comfort.
This object is achieved according to one embodiment of the present invention by providing a patient interface and exhaust assembly in which the patient interface assembly includes a faceplate having a first opening defined in a first end and a second opening defined in a second end thereof. A seal associated with the second opening is provided for contacting a surface of the patient, with the faceplate, seal, or both defining an interior of the patient interface assembly. A patient circuit is coupled to the first opening to communicate with an interior of the patient interface assembly. In this embodiment, the exhaust assembly is provided at the interconnection of the faceplate and patient circuit, and includes an exhaust path defined generally between the faceplate and the patient circuit and a flow regulating member. In another embodiment of the present invention, the exhaust assembly is incorporated into the mask shell or faceplate itself with the exhaust path being defined between portions of the faceplate and between the flow regulating member and a portion of the faceplate.
In either embodiment, the flow regulating member controls the rate of flow of exhaust gas passing to atmosphere through the exhaust path by being deformed into the exhaust path varying degrees. The degree of deformation of the flow regulating member into the exhaust path is based on a pressure in the interior of the patient interface assembly relative to ambient atmospheric pressure. More specifically, the flow regulating member responds to the different pressures applied to its opposite sides to vary the effective cross sectional area of the exhaust path. With relatively higher pressure within the patient interface relative to ambient atmosphere pressure, the flow regulating member flexes and deforms into the flow path, thereby narrowing the exhaust path and thus reducing its effective cross sectional area.
The amount of narrowing of the exhaust path, and, thus, the amount of cross sectional area reduction, varies with variation in the elevated pressure within the patient interface. Higher pressures in the patient interface produce greater exhaust path area reduction and lower pressures produce smaller flow path area reduction. By providing a greater exhaust path area reduction in the presence of high patient circuit pressures and a lower exhaust path area reduction in the presence of lower patient circuit pressure, the flow rate of the exhaust gas can be kept substantially constant over these ranges of pressures in the patient circuit. Because the flow regulating member can flex to an infinite number of positions with incremental changes in the elevated gas pressure within the patient interface, the cross sectional area of the exhaust path can be any of a corresponding infinite number of values. Hence, with this exhaust valve assembly it is possible to provide relatively constant exhaust flow over a continuous range of operating pressures. It is also possible to provide other flow rate profiles over the range of operating pressures, such as a decreased flow as pressure increases, that cannot be achieved by a fixed size leak.
Further objects of the present invention are to provide a system and method for providing a supply of breathing gas to an airway of a patient that makes use of the combined patient interface and integrated exhaust assembly.